A high-pressure furnace that operates up to 2000°C in the pressure range of 100 atm to 10−5 torr was designed and constructed to saturate UO2 powder of 4-µm average particle size with 4He. The powder was then dissolved in a fused salt in an induction chamber. The released 4He was mixed with a known quantity of 3He, and the mixture was analyzed with a mass spectrometer to determine the 4He: 3He ratio, hence the original mass of 4He in the sample. The solubility of He in UO2 at 1200 and 1300°C was found to be 6.71 × 10−4 and 3.23 × 10−4 cm3 (STP)/(g atm), respectively. It was also found that the He-UO2 system obeys Henry's law. From a plot of He concentration as a function of time, the diffusion coefficient at 1200 °C was estimated to be 1.5 × 10−13 cm2/sec.